Zhu, Guodong., Hong, Ikjun., Li, Kewei., Anyika, Theodore., Ugwu, Maxwell T., Nolen, Joshua Ryan., He, Mingze., Caldwell, Joshua David., & Ndukaife C, Justus C. (2025). Engineering Thermal Emission with Enhanced Emissivity and Quality Factor Using Bound States in the Continuum and Electromagnetically Induced Absorption. Advanced Optical Materials. Advance online publication. https://doi.org/10.1002/adom.202501257
Metal-based thermal metasurfaces are special materials designed to control how heat is emitted as light. Unlike traditional materials—such as gray-bodies, near–black bodies, or some dielectric metasurfaces—these metal-based structures keep their emission patterns stable even when temperatures change. However, they often have a major drawback: they lose a lot of energy internally through ohmic losses, which limits their quality (Q) factor, a measure of how sharp and selective their emission is.
This study focuses on solving that problem by finding a way to achieve both high emissivity (how effectively a material emits thermal radiation) and high Q factors in metal-based thermal emitters. The researchers use a design strategy that combines three surface lattice resonances. These resonances support special physical effects called bound states in the continuum and electromagnetically induced absorption (EIA), which together allow the structure to emit light very efficiently and at very specific wavelengths.
Using simulations, the team designed a metal-based metasurface that achieves near-unity emissivity (0.96) and a Q factor of 320. Experiments confirmed strong performance, showing an emissivity of 0.82 and a Q factor of 202—about five times better than the best previously reported metal-based thermal metasurfaces.
Overall, this work demonstrates a promising way to create efficient, narrow-band, and directional thermal emitters that maintain stable performance even across large temperature changes.
Figure 1
Schematic of the metal-insulator-metal (MIM) configuration used in the study. a) shows the schematic of the thermal metasurface for narrowband directional thermal emission. b) shows the top view of a unit cell of the metasurface comprising a complete circular gold ring and a segmented gold ring. c) shows the side view of a unit cell. A 150 nm gold reflector is thick enough to prevent optical transmission, and a 150 nm aluminum oxide spacer is used to maximize the emission.